The MAPIUID structure identifies which address book provider supplies this particular container in the container hierarchy. The value is unique to each provider.

An address book provider can provide more than one identifier. For example, a provider that supplies two different containers can publish in PR_AB_PROVIDER_ID unique identifiers for each container.

PR_AB_PROVIDER_ID is analogous to the PR_MDB_PROVIDER (PidTagStoreProvider) property for message stores. Client applications can use PR_AB_PROVIDER_ID to find related rows in an address book hierarchy table.